Human Physiology/The Urinary System PDF

Lec 8 Safiya saad Human Physiology/The Urinary System Introduction The Urinary System is a group of organs in the body concerned with fi...

Lec 8 Safiya saad Human Physiology/The Urinary System Introduction The Urinary System is a group of organs in the body concerned with filtering out excess fluid and other substances from the bloodstream. The substances are filtered out from the body in the form of urine. Urine is a liquid produced by the kidneys, collected in the bladder and excreted through the urethra. Functions of the Urinary System 1- Excretion. Excretion is the process of eliminating, from an organism, waste products of metabolism and other materials that are of no use. 2- Maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine. 1  Lec 8 Safiya saad 3- Regulating the concentrations of various electrolytes in the body fluids and maintaining normal pH of the blood. The Urinary organs include 1- Kidneys 2- Ureters 3- Bladder 4- Urethra. Six important roles of the kidneys are: Regulation of plasma ionic composition. Ions such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphates are regulated by the amount that the kidney excretes. Regulation of plasma osmolarity. The kidneys regulate osmolarity because they have direct control over how many ions and how much water a person excretes. Regulation of plasma volume. Your kidneys are so important they even have an effect on your blood pressure. The kidneys control plasma volume by controlling how much water a person excretes. The plasma volume has a direct effect on the total blood volume, which has a direct effect on your blood pressure.. Regulation of plasma hydrogen ion concentration (pH). The kidneys partner up with the lungs and they together control the pH. The kidneys have a major role because they control the amount of bicarbonate excreted or held onto. The kidneys help maintain the blood pH mainly by excreting hydrogen ions and reabsorbing bicarbonate ions as needed. 2  Lec 8 Safiya saad Removal of metabolic waste products and foreign substances from the plasma. One of the most important things the kidneys excrete is nitrogenous waste. As the liver breaks down amino acids it also releases ammonia. The liver then quickly combines that ammonia with carbon dioxide, creating urea which is the primary nitrogenous end product of metabolism in humans. The liver turns the ammonia into urea because it is much less toxic. The creatinine comes from the metabolic breakdown of creatine phospate (a high-energy phosphate in muscles). Uric acid comes from the break down of nucleotides. Uric acid is insoluble and too much uric acid in the blood will build up and form crystals that can collect in the joints and cause gout. Secretion of Hormones The endocrine system has assistance from the kidney's when releasing hormones.  Renin is released by the kidneys. Renin leads to the secretion of aldosterone which is released from the adrenal cortex. Aldosterone promotes the kidneys to reabsorb the sodium (Na+) ions.  The kidneys also secrete erythropoietin when the blood doesn't have the capacity to carry oxygen. Erythropoietin stimulates red blood cell production.  The Vitamin D from the skin is also activated with help from the kidneys. Calcium (Ca+) absorption from the digestive tract is promoted by vitamin D. 3  Lec 8 Safiya saad Organs in the Urinary System  The kidneys are a pair of bean shaped, brown organs about the size of your fist. It measures 10-12 cm long.  They are covered by the renal capsule, which is a tough capsule of fibrous connective tissue. Adhering to the surface of each kidney is two layers of fat to help cushion them.  There is a concaved side of the kidney that has a depression where a renal artery enters, and a renal vein and a ureter exit the kidney.  The kidneys are located at the rear wall of the abdominal cavity just above the waistline, and are protected by the ribcage.  There are three major regions of the kidney, renal cortex, renal medulla and the renal pelvis.  The outer, granulated layer is the renal cortex. This contains pyramid shaped tissue called the renal pyramids, separated by renal columns. 4  Lec 8 Safiya saad  The ureters are continuous with the renal pelvis and is the very center of the kidney. Ureters  Two tubes that drain urine from the kidneys to the bladder.  A muscular tube. Muscles in the walls of the ureters send the urine in small spurts into the bladder, (a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine). After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra. 5  Lec 8 Safiya saad Urinary Bladder 1. A hollow, muscular and distendible or elastic organ that sits on the pelvic floor. 2. The posterior border, the vagina (in females) and rectum (in males). 3. The urinary bladder can hold approximately (500 to 530 ml) of urine, however the desire to micturate is usually experienced when it contains about 150 to 200 ml. 4. When the bladder fills with urine (about half full), stretch receptors send nerve impulses to the spinal cord, which then sends a reflex nerve impulse back to the sphincter (muscular valve) at the neck of the bladder, causing it to relax and allow the flow of urine into the urethra. 5. The Internal urethral sphincter is involuntary. 6. The urine in the bladder also helps regulate body temperature. 6  Lec 8 Safiya saad Urethra  A muscular tube that connects the bladder with the outside of the body.  The function of the urethra is to remove urine from the body.  It measures about 1.5 inches (3.8 cm) in a woman but up to 8 inches (20 cm) in a man.  Because the urethra is so much shorter in a woman it makes it much easier for a woman to get harmful bacteria in her bladder this is commonly called a bladder infection or a UTI. The most common bacteria of a UTI is E-coli from the large intestines that have been excreted in fecal matter.  The length of a male's urethra, and the fact it contains a number of bends, makes catheterisation more difficult. The urethral sphincter is a collective name for the muscles used to control the flow of urine from the urinary bladder. These muscles surround the urethra, so that when they contract, the urethra is closed.  There are two distinct areas of muscle: the internal sphincter, at the bladder neck and  The external, or distal, sphincter. Human males have much stronger sphincter muscles than females, meaning that they can retain a large amount of urine for twice as long, as much as 800mL, i.e. "hold it". 7